Track bushing wear reducing device

ABSTRACT

AN IMPROVED ENDLESS TRACK DEVICE IS PROVIDED FOR PREVENTING AN EARLY WEAR OF TRACK BUSHES AND SPROCKETS, WHICH DEVICE IS CHARACTERIZED IN THAT PROJECTIONS ARE PROVIDED AT INSIDE ENDS OF TRACK LINKS AND NOTCHED PORTIONS ARE ALSO PROVIDED AT BOTH ENDS OF TOOTH TIPS OF SPROCKETS, AND THAT IN A LOCALITY WHERE THE TRACK LINKS AND SPROCKETS COME INTO ENGAGEMENT WITH EACH OTHER AT THE TIME OF DRIVING THE TRACK IN A REVERSE DIRECTION, THESE PROJECTIONS ARE ENGAGED WITH THE NOTCHED PORTIONS ONLY IMMEDIATELY BEFORE SAID ENGAGEMENT TO THEREBY PREVENT CONTACT BETWEEN PERIPHERAL SURFACE OF THE BUSH AND THE TOOTH SURFACE OF THE SPROCKET.

United States Patent I I I Inventor Teruo Furukawa Sagamihara-shi, Japan Appl. No. 788,241

Filed Dec.3l,l968

Patented June 28, I971 Assignee Caterpillar Mitsubishi Ltd.

Tokyo, Japan Priority Jan. 9, 1968 Japan 43/665 TRACK BUSHING WEAR REDUCING DEVICE I Claim, 10 Drawing Figs.

U.S. CI 305/57,

305/58 Int. Cl 862d 55/20 Field of Search 305/57, 58

{56] References Cited UNITED STATES PATENTS l,54l 026 6/l925 Blewett 305/57 2,003,528 6/1935 Best 305/57 Primary Examiner-Richard J. Johnson AttorneyWenderoth, Lind & Ponack ABSTRACT: An improved endless track device is provided for preventing an early wear of track bushes and sprockets, which device is characterized in that projections are provided at inside ends of track links and notched portions are also provided at both ends of tooth tips of sprockets; and that in a locality where the track links and sprockets come into engagement with each other at the time of driving the track in a reverse direction, these projections are engaged with the notched portions only immediately before said engagement to thereby prevent contact between peripheral surface of the bush and the tooth surface of the sprocket.

PATENTHHUHEMSH 3588195 SHEET 1 BF 4 TERUO FURUKAWA,

Inventor YJUMMZXJQM Attorneys PATENTEU JUN28 [9H SHEET 2 BF 4 TERUO FURUKAWA,

' INVENTOR y $02. LQMUZXJZ MW Attorneys PATENTEDJUN28l97l 3588.195

sum 3 0F 4 'IERUO FURUKAWA,

Inventor Attorneys PATENTEUJUNZBIHY! 3.588.195

SHEET 0F 4 'TERUO FURUKAWA,

MJMAM M-LMM Attorneys TRACK BUSHING WEAR REDUCING DEVICE It is well known that an endless track device is used on track-type tractors or leaders and the like, which are employed in civil engineering and construction works. Some parts of the endless track device undergo drastic wear owing to soil, sand and the like because these machines are driven under severe conditions. in particular, the wear of track bushes and sprockets is serious as compared with other parts. After the machine has been operated for a certain period of time, the endless track is entirely disassembled and repaired. But the above-mentioned parts cannot withstand wear until the time of repair. Hence, before such time, it is necessary to rotate the track bushes and pins, and use their unwom surfaces.

Attempts to prevent wear of the track bushes and track pins have been proposed heretofore. For instance, a seal is provided on both ends of a track bush so as to prevent the entry of soil and sand. By so doing, the wear of the inner surface of the bush and the outer surface of the pin, which surfaces rotate in contact with each other, has been greatly reduced. On the other hand, the lives of the outer surface of the track bush and sprocket teeth have been prolonged to some extent by improving the quality of materials that make up these parts or by improving the heat treatment procedure. These are, however, not yet satisfactory. in accordance with the present invention, it has been found that the wear of track bushes and sprockets is ascribable to the structure of a track bush and the mechanism of engaging the track bush with the sprocket. When the vehicle goes backwards, track bushes and sprocket teeth on the reverse driving side undergo wear at an early stage. In contrast, on the forward driving side, the wear of the outer surfaces of track bushes and sprocket teeth is about half of that on the reverse driving side in spite of a larger driving force. Based on the foregoing, and in accordance with the present invention, the shapes of a track link and a sprocket have been changed so that the outer surface of the bush does not come into direct contact with the sprocket teeth at the upper portion of the sprocket, thus preventing an early wear of the parts.

The purpose of the present invention is therefore to prevent an early wear of track bushes and sprockets, and prolong their lives to twice those of the conventional ones.

The invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a side elevation of some of the tracks and sprockets on the right side of the endless track device of the invention;

FIG. 2 is a sectional view taken along the line 2-2 of FIG. I;

FIG. 3 and 4 are a plan view ofa part of the track;

FIG. 5 is a view showing the relation between sprockets and bushes;

FIG. 6 is a view showing the wear of a track bush;

FIG. 7 is an enlarged view of FIG. 1 showing the relation between bushes and sprockets;

FIG. 8 is a front elevation ofa track link;

FiG. is a perspective view of an end portion of the track link; and

FIG. 10 is a reference diagram showing a projection forming range at the end rim of the track ring.

Referring to FIG. 6, an arrow A shows a forward direction of the tractor, and an arrow B, a reverse direction. it has been empirically confirmed that the wear of the surface of bush 2 is about twice as serious in the direction of arrow A as that in the direction of arrow B. Much the same wear is observed also at the bottom surfaces of the sprocket teeth. It can be conjectured that both in the forward and reverse movements of the track, the contact surface of bush 2 and the tooth surface of sprocket 8 undergoes a slight wear at an early stage because of a slight deviation of both or of the presence of foreign materials on the contact surface. If this conjecture is correct, the wear on the forward driving side must be greater than that on the backward driving side since u far greater driving force act on the forward driving side than on the reverse driving side. in fact, however, as shown in FIG. 6. the wear is more drastic in the case of driving in the reverse direction, and there must be another cause for it To illustrate this cause, reference will now be made to FIGS. 4 and 5. A track consists of links 3 on both sides, a bush 2 associating both sides, and a pin l extending through said bush 2. The links 3 on both sides are connected with each other by the bush 2 and pin I. As shown in FIG. 4, the bush 2 is force fitted to the links 3 on both sides at position m, and held between outside portions ofthc tips of subsequent links (on the side of an arrow B). Thereafter, a pin 1 is inserted into the bush 2 so that the pin 1 may rotate facing the inner surface of bush 2. The end of the pin 1 is fitted into the tip of the subsequent link 3. Thus, each set of links integrated via the bush at the rear end can rotate with the pin as a pivotal axis. A track consisting of many links in the above-mentioned manner is driven both in the forward direction shown by an arrow A and in the reverse direction shown by an arrow B. The arrow B in FIG. 5 indicates a direction in which the sprocket rotates when the track is driven in the reverse direction. in this FlG., the bush 2 is connected with the pin 1 by a dotted line in order to show that they are integrated via the links on both sides. Sets of tracks connected by dotted lines are designated by a, b and c respectively. First, set a is driven by a sprocket 8, and advances to the position where set b is situated. When this occurs, two questions arise. First, in what condition does bush 2 come into engagement with the tooth surface of sprocket 8?Second, what is the cause whereby the wear of the surface of bush 2 occurs specifically in most cases at the time of backward movement'l'l'horough observation will be made as below-mentioned relative to these problems.

In FIG. 5, when sprocket 8 rotates in the direction 8' to cause track set a to be driven in the reverse direction and displaced to the position of set b, track set a initially takes the position such that a line connecting the centers of bush 2 and following pin 1 is horizontal while a line connecting the centers of bush 2 and thesprocket is vertical. Namely, bush 2 is considered to take a position just above sprocket 8. The horizontal and vertical lines intersect at the central point of bush 2. Track set a is in the position that bush 2 will initially receive the driving force from sprocket 8. in the positions as above described, the following assumption will be further established for convenience of explanation. First, track set a is assumed to be in an independent condition i.e. to be released from coupling with the preceding and following links. if it is assumed that bush 2 advances to a position designated set b with the rotation of sprocket 8 while maintaining the relative position between track set a and sprocket 8 in the condition as above described, the track would take the position as designated by the dotted line b. This is because the relative position of track set b to the axial center of sprocket 8 is identical with that of track set a. in other words, if the independent track set a is rotated around the axial center of sprocket 8, it takes the position of b. Attention should be drawn to the fact that during the time when track set a is displaced to the position of track set b, no deviation will take place between bush 2 and the tooth surface of sprocket 8. Consequently, it may be considered that almost no wear is caused to take place between bush 2 and the tooth surface of sprocket 8. The above mentioned is an assumption and as a matter of fact, since track set a is coupled with the forward and backward links, track set a advances to the position of track set b when it moves backward. As is evident from a comparison of track set b with track b, they are on the same axis of bush 2, but the positions of the pins are different. In order for track b to take the position of track b, the pin is caused to move from I to l centering around bush 2, i.e. bush 2 is slightly rotated. This rotation gives rise to a friction between bush 2 and the tooth surface of the sprocket. The said rotation takes place gradually as track set 0 moves to track set b. The total extent of this rotation is shown by u in FIG. 5. u= 12- lfl. As above mentioned. the following pin l rotates the preceding bush 2 and in this case, bush 2 contacts the tooth surface of the sprocket and slides by the said angle, thus causing wear to take place. The said rotation of bush 2 occurs solely during the time when the track changes its position from set a to set b. In other instances, such as for example a shift from set b to set c, the rotation of bush 2 as aforesaid does not occur.

In general, when pebbles and other foreign materials are inserted between the tooth surface of sprocket and bush 2, wear is caused to take place on the surface of bush 2. This is shown in FIG. 6. It is reasonable to assume that the cause of more wear on the surface of bush 2 when the sprocket 8 rotates specifically in the direction B is the rotation of bush 2 as above discussed.

In contrast, the question arises as to whether this rotation of bush 2 occurs during forward movement of the track. At the time of forward movement, engagement begins to occur at the lower part of sprocket 8. In the case such as for example in FIG. 5, sprocket 8 rotates in a direction opposite to arrow B and the track advancing horizontally comes into engagement with sprocket 8 at the lower part of the sprocket and then the track gradually shifts in the upward direction. At this time, in each track the pin precedes and the bush follows. When the preceding track changes its position upwardly, rotation before and after it is always conducted between the bush and the pin. Thus, there is no rotation between the bush and the tooth surface of the sprocket contrary to the case of the abovedescribed backward movement.

As is evident from the foregoing, the cause of this specific wear on the peripheral surface of the bush during backward movement has been brought to light. One of the most critical points in this connection resides in the fact that the portions where wear occurs are places where track set a moves backwards to shift its position to that of track set b as illustrated in FIG. 5. The direct cause of wear is the rotation of bush 2 contacted with the tooth surface of sprocket 8. This invention has the following solution for preventing this wear. Namely, the surface of bush 2 and the tooth surface of sprocket 8 are devised so as not to come into engagement while bush 2 rotates as above described. When bush 2 of track set a and the tooth surface of the sprocket are about to contact, a portion adjacent bush 2 of track set a is pushed up with the tooth end of the sprocket whereby the bush and the tooth are maintained out of contact with each other. When set a has advanced to the position of track set b, this separation is released. As above explained, the track is pushed up during the time when each track moves backwardly by one pitch from the position of just above sprocket 8, thereby keeping the tooth surface and the bush apart from each other. This is the main point of the present invention and is described in more detail below.

As is illustrated in FIGS. 7, 8 and 9, a projection 9 is provided on the inner side of one end of each track link 3. The position of projection 9 is predetermined to be on the peripheral rim of the opening for the bush at the forward end of the link when the track moves backwards.

As illustrated in FIG. 10, when a line connecting the centers of the two openings in a link is a 270 line, the projection 9 is provided on the periphery of the opening in a range of from 270 to 330. A notched portion 10 is provided at both sides of the tooth tip as illustrated in FIGS. 2 and 7. The combination of the said notched portion with the projection 9 is shown in FIGS. 2 and 7. In FIG. 7, when bush 2 of track set a is situated directly above sprocket 8, the notched portion 110 at the tooth tip of the sprocket pushes up the projection 9 on the inner side of one end of link 3. If this projection is not provided, contact will occur between the tooth surface 8' of the sprocket and the surface of bush 2. However, since projection 9 is provided on the side end of link 3, the notched portion 10 of the tooth tip contacts with the lower surface of projection 9 and pushes up the track thereby forming a suitable narrow gap between the peripheral surface of bush 2 and the tooth surface 8' confronting thereto. It has been empirically proved that a preferable size of the said narrow gap should be approximately 3 mm.-5 mm.

Concerning forms of projection 9, any form will do as long as the projection 9 contacts with the notched portion 10 of the tooth tip to lift the bush and thus form the gap I5 between the tooth surface 8' and the peripheral surface of the bush. As illustrated in the embodiment of FIG. 9, the projection may be made so as to be capable of contacting with the notched portion I0 of the sprocket by providing an inclined surface I3 having a predetermined degree of slope on the upper surface of projection 9 and a horizontal surface II on the lower surface thereof. The projection may be integrally molded with the link or separately manufactured and then suitably attached to the link.

In the present invention, the sizes of the projection 9 and notched portion It) should be determined so as to provide a gap between them as mentioned above. If a gap is not formed between the peripheral surface of a bush 2 and the tooth surface of a sprocket 8 owing to a projection 9 being too small or a notched portion I0 being too large, the objects of the invention cannot be achieved. It is not necessary that the projection 9 should be pushed by up the notched portion 10 and continuously maintained in this condition. Instead, the projection 9 must be apart from the notched portion 10 when the bush 2 of set a has been completely engaged with the sprocket 8, for instance, When set a has moved to the position of set b.

Now, the operation of the invention will be discussed.

As shown by an arrow B in FIG. I, sprocket 8 rotates, and the track is driven in the reverse direction. At an early stage of meshing of the track bush and the sprocket, projection 9 and notched portion 10 provided with a predetermined range, contact each other to provide a gap of approximately 3-5 mm. between the peripheral surface of the track bush 2 and the tooth surface of the sprocket 8. When the sprocket 8 rotates in the direction of an arrow B in this state, the preceding portion of the track takes a downward course while maintaining the gap, whereby the following bush 2 rotates slightly. During this rotation, the engagement between the projection 9 and the notched portion 10 is not released. That is to say, a suitable gap is maintained between the peripheral surface of the bush 2 and the tooth surface of the sprocket 8, and at least during the above-mentioned rotation, both surfaces are prevented from contacting each other. Thus, the wear caused by friction between the peripheral surface of the bush 2 and the tooth surface of the sprocket 8 is eliminated because the bush 2 is entirely in the lifted state. As already mentioned, when the meshing between the track bush 2 and the tooth of the sprocket 8 is completed, the projection 9 is apart from the notched portion 10.

Now, consideration will be made as to whether the practice of the invention wall cause any problems during power transmission. In the case of driving in the reverse direction, it is only during the very early stages (0 in FIG. 7) of meshing between the track and the sprocket that the projection 9 comes into engagement with the notched portion 10 at the upper half of the track. When both are in normal engagement (0 in FIG. 7) with each other, the track bush 2 comes into contact with the tooth surface of the sprocket 8, and the driving power of the sprocket 8 is transmitted to the track via the bush 2. Thus, no trouble occurs in the operation in the upper half of the sprocket when the track is driven in the reverse direction. At the lower half of the sprocket, the track link 3 in the bended state is stretched in a direction tangential to the sprocket 8. At this time, the track bush 2 does not contact and slide with the sprocket 8, but the track pin 1 moves. Namely, the inner surface of the track bush 2 contacts and slides with the outer surface of the track pin 1. The gap between the projection 9 and the notched portion It) gets larger and larger, and they do not contact each other.

Discussion will now be directed to the forward movement of the vehicle in which the sprockets 8 rotate in a direction opposite to that shown by an arrow B of FIG. 1. At the upper half of the sprocket 8, the track line 3 in the bended state is stretched in a tangential to direction the sprocket 8. At an early stage of this change of direction, the projection 9 contacts the notched portion l0. Shortly, they part from each other, with an increasing gap between them. In this case, the movement of the track link 3 is mainly dominated by the following bush 2, and the peripheral surface of the bush 2 slides with the tooth surface of the sprocket 8. A driving force does not directly act on this portion of the track.

Regarding the lower half of the sprocket 8 at the time of forward movement, a large driving force acts between the sprocket and the track bush, but contrary to the case of reverse movement, the pin precedes the links and bush. Therefore, the projection 9 and notched portion 10 on the side of the bush are initially apart from each other, and gradually come closer to each other. Even when the bush 2 meshes with the tooth surface of the sprocket 8, there is some space between the projection 9 and the notched portion 10. At this time, by the movement of the track link 3, the inner surface of the bush of the preceding link slides with the peripheral surface of the pin 1 of the following link. It is therefore appreciated that the practice of the present invention causes no disruption in the operation of the vehicle.

Finally, the strength of the projection 9 will be considered. The driving force at the time of reverse movement of the vehicle is smaller than that at the time of forward movement. Hence, a component in a radical direction of the driving force at the projection 9 is very small when the bush begins to be meshed with the sprocket during reverse driving, and the contact pressures on the projection 9 and notched portion [0 are also very small. Consequently, it will be appreciated that the projection 9 of the invention is not readily damaged, and

withstands use for a considerable length of time.

It is an advantage of the present invention that by improving a part of the conventional endless track mechanism, an early wear of the peripheral surface of track bushes and tooth surfaces of sprockets on the reverse driving side is prevented, and the lives of the bushes and sprockets are prolonged to twice those of conventional device.

The invention is not restricted by the embodiment given above, and various changes and modifications are possible without departing from the spirit of the invention.

I claim:

I. In an endless track device comprising links, pins and bushes coupled together to form an endless double-link track, said links having openings at each end to receive said bushes, and sprockets having teeth thereon and mounted to mesh with said endless track to drive said endless track in either a forward or a reverse direction; the improvement comprising projections provided on the inner sides of said links around the peripheries of said openings on the ends of said links toward said reverse direction, said projections being on the side of a line between said openings away from said sprockets, and notched portions provided on both edges of the outer tips of said teeth of said sprocket; the arrangement being such that when said device moves in said reverse direction, said n otc hed portions contact and lift said projections only during initial engagement between said sprockets and said endless double-link track. 

